While in-memory databases have their uses, it kneecaps
    SQLite into something far less useful. To build any
    kind of app with it, we need the ability to write and
    persist.

Another approach than writing the data to a server could be to allow the user to store it on their own hard disk.

This could be done via the File System Access API:

https://developer.mozilla.org/en-US/docs/Web/API/File_System...

The API already works nicely in Desktop Chrome:

https://googlechromelabs.github.io/text-editor/